This invention relates to a database management system and a storage system. More specifically, this invention relates to a technique of reconstructing data by employing a journaling technique of a storage system.
In connection with popularization of utilization of databases in corporate activities, data reconstructing techniques constructed of back-up techniques and recovery techniques have been widely utilized in order to avoid data stored in the databases from being lost. A back-up operation of a database implies such a technical idea that data stored in the database are duplicated in a storage device such as a storage tape device in a periodic manner. A recovery operation of a database implies such a technical idea that back-up data recorded on a storage tape, or the like are first restored in the database. Thereafter, a record (will be referred to as “log” hereinafter) of changed data of from a time instant when the data were backed up in the restored database up to now, or until a certain past time instant is applied so as to reconstruct the database under such a status that consistency of a transaction is secured. A log is generated by a database management system, and indicates a history of changing operations with respect to the database.
In recent years, in order to shorten time required for restoring databases, a specific attention has been paid to database reconstructing methods using journaling techniques. This journaling technique is also called as a continuous data protection (CDP) technique, and is disclosed in, for example, JP 2004-252686 A. In the technical idea disclosed in JP 2004-252686 A, in the storage system, while both the database and the log are stored in the same storage device, every time the update instruction for the data is received, the update history (will be referred to as “journal” hereinafter) is recorded in another storage device (will be referred to as “journal storage device” hereinafter).
Also, the database management system executes a check point process operation in order that data stored in a buffer of the database management system is made coincident with data stored in a storage system. When the database management system finishes the check point process operation, the storage system receives a check point command from the database management system, and generates a journal in correspondence with identification information of the check point, and then records the generated journal in the journal storage device.
When the storage system receives a restore instruction containing the identification information of the check point from the database management system, the storage system restores the database and the log at high speed by employing a journal recorded in the journal storage device before the journal corresponding to the identification information of the check point contained in the restore instruction. Then, when the restoring operations of both the database and the log are finished, the database management system applies the log to the database to secure the transaction consistency, and then finishes the recovery operation of the database.